class_docstr: A class representing group homomorphisms. Instantiate using `homomorphism()`.
  
  References
  ==========
  
  .. [1] Holt, D., Eick, B. and O'Brien, E. (2005). Handbook of computational group theory.
docstr: Compute the kernel of `self`.
docstr_tok: ["Compute","the","kernel","of","`","self","`","."]
code: def kernel(self):
      """
      Compute the kernel of `self`.
  
      """
      if self._kernel is None:
          self._kernel = self._compute_kernel()
      return self._kernel
  
imports: import itertools
  from sympy.combinatorics.fp_groups import FpGroup, FpSubgroup, simplify_presentation
  from sympy.combinatorics.free_groups import FreeGroup
  from sympy.combinatorics.perm_groups import PermutationGroup
  from sympy.core.intfunc import igcd
  from sympy.ntheory.factor_ import totient
  from sympy.core.singleton import S
label_desc: Use image node_id 4 for calling the GroupHomomorphism obj's underlying member method code with example usage: obj.kernel() and returns: self